An autofocus function for automatically adjusting the focus on a subject is incorporated in wide variety of image capture apparatuses such as cameras for convenience of user. A focus detecting apparatus implementing such a autofocus function detects the state of focus of the photographing lens and a defocus amount by which the photographing lens is out of focus so that the automatic adjustments of the focus can be made accordingly.
In a conventional camera, an error may occur in detecting the focus state of a lens due to the chromatic aberration that may result from the differences in the reflective index of various light illumination sources according to the respective wavelengths. For example, in general, it may be preferable to take the focus of a subject based on a wavelength (approximately 587 nm) of green which is most sensitive to the human eye. However, the wavelength component of the light source illuminating the subject may changes according to the surrounding environment. As a focus detecting apparatus detects the focus state of the photographing lens based on the light projected onto the focus detecting apparatus, if the main wavelength component of the light source illuminating the subject is significantly different from the wavelength of green, a precise focusing on the subject may be difficult.
In an environment without sufficient light illumination, a supplemental or external light source, e.g., a flash light, may be used. In those situations, infrared light sources are generally used as the supplemental light source. However, since the wavelength of infrared rays deviates significantly from the wavelength of green, the use of such supplemental light source may exacerbate the imprecision in the detection of the focus state of the lens.
While some prior attempts to address the various types of light illumination with respect to focus detecting apparatuses have been made, these attempts fail to adequately compensate for the variation in the light illumination, and may require many additional components to determine the type of light source or illumination, which in turn may result in the increase in the manufacturing cost, lowered productivity and the increase in the overall size of the image capture apparatus.